Accessing Service Desk externally

Accessing Service Desk externally

We wish to make Service Desk accessible to our remote users externally. We are trying to crete a rule in the ISA Firewall to allow the connection through. However, when we try to connect to Service Desk we are prompted by a Windows login box. Is there any way to get round this so that users are directed straight to the Service Desk login page instead. If we set the rule in ISA for internal access only, we get through without a prompt. Can anyone shed some light on this for me please.
Many thanks

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